Add new Kaniko Dockerfile for PDNS builder.

Put it besides `Dockerfile-kaniko` until it is clear that one can be
removed.

Dockerfile-kaniko-pdns-builder

@@ -0,0 +1,19 @@
+FROM gcr.io/kaniko-project/executor:v1.12.0-debug AS kaniko
+
+FROM alpine:3.11
+
+RUN apk --no-cache add bash binutils coreutils git grep openssh-client perl rsync sed tree
+
+COPY --from=kaniko /kaniko /kaniko
+COPY --from=kaniko /etc/nsswitch.conf /etc/nsswitch.conf
+COPY --from=busybox:musl /bin /busybox
+
+ENV HOME /root
+ENV USER root
+ENV PATH $PATH:/kaniko:/busybox
+ENV SSL_CERT_DIR /kaniko/ssl/certs
+ENV DOCKER_CONFIG /kaniko/.docker/
+ENV DOCKER_CREDENTIAL_GCR_CONFIG /kaniko/.config/gcloud/docker_credential_gcr_config.json
+ENV GOOGLE_APPLICATION_CREDENTIALS='/kaniko/.docker/config.json'
+
+ENTRYPOINT ["/kaniko/executor"]

README.md

@@ -243,3 +243,33 @@ For example, if the base image you use upgrades the compiler, the compiled outpu
 will likely change.
 
 
+## Custom Kaniko Image for PDNS Builder
+
+https://hub.docker.com/repository/docker/powerdns/kaniko-pdns-builder/
+
+A custom Kaniko image for PDNS Builder, because the official Kaniko debug image only offers Busybox and the PDNS Builder also needs Bash, Git, Perl, rsync and perhaps more.
+
+### Building
+
+- `docker build -f Dockerfile-kaniko-pdns-builder -t powerdns/kaniko-pdns-builder:1.0.0 .`
+
+### Distributing
+
+- `docker tag powerdns/kaniko-pdns-builder:1.0.0 powerdns/kaniko-pdns-builder:latest`
+- `docker push powerdns/kaniko-pdns-builder:1.0.0`
+- `docker push powerdns/kaniko-pdns-builder:latest`
+
+### Running
+
+- `docker run -it --entrypoint warmer powerdns/kaniko-pdns-builder:1.0.0 bash`
+- `docker run -it powerdns/kaniko-pdns-builder:1.0.0`
+
+### Resources
+
+From:
+
+- https://github.com/GoogleContainerTools/kaniko/blob/main/deploy/Dockerfile
+- https://hub.docker.com/r/pernodricard/kaniko-alpine/dockerfile
+- https://stackoverflow.com/a/69251129
+
+- `curl --silent https://gcr.io/v2/kaniko-project/executor/tags/list | jq .`